Method for the preparation of cellulose ethers



Patented Mar. 8, 1938* UNETED STATES METHOD FOR THE PREPARATION OFCELLULOSE ETHEES Eugene J. Lorand, Wilmington, Del., assignor toHercules Powder Company, Wilmington, Del, a corporation of Delaware NoDrawing. Application January 9, 1937,

Serial No. 119,783

12 Claims.

a method for the alkylation of cellulose in the.

presence of an aliphatic alcohol.

As is well known, alkyl ethers of cellulose are produced by the actionof an alkylatlng agent, such as, an alkyl halide, on a'cellulose in thepresence of an alkali, such as caustic soda, in the presence of more orless water. Heretofore, the addition of alcohol to the reaction mixturehas been suggested. Thus, U. S. Patent 1,188,376 suggests the alkylationof cellulose in the presence of an aqueous-alcoholic solution ofcaustic. The use of alcohol has in general been-'foundto bedisadvantageous in the alkylation of cellulose, since the alcohol reactswith the alkylating agents in the presence of caustic alkali, thusdecreasing the amount of alkylating agent present for reaction with thecellulose. The result of the use of alcohol in the alkylation ofcellulose has been incomplete alkylation in spite of very highconsumption of the alkylating agent, lack of uniformity and a degradedproduct.

I have found that the use of alcohol in the alkylation of celluloseunder different and limited conditions avoids the undesirable resultsusually obtained by the use of alcohol, and makes possible theetherification of cellulose in a much shorter time than used heretofore,or in the same time at a lower temperature. A further advantage is anincreased yield which may be 10 to 20% higher than that obtained in theprocesses used heretofore.

The method in accordance with this invention calls for reactingcellulose with an alkylating agent in the presence of an aliphaticalcohol in amount within the range of about 2.0% to about by weight ofthe cellulose present. I prefer to restrict the amount oi alcohol to anamount within the range of about 40% to about 70% of the weight of thecellulose. The alcohol willdesirably .contain the same alkyl group asthat contained in the alkylating agent, and will desirably besubstantially anhydrous, althougha moderate water content is notobjectionable. Water may also be present as moisture in the cellulose.The maximum total water content or the reaction mixture will desirablybe not more than and preferably not more than 30% of the weight ofcellulose used. The alkylating agent used may be an alkyl halide or analkyl sulphate and preferably an alkyl chloride. Thus, for example, thealkylating agent may be ethyl chloride, ethyl bromide, butyl chloride,butyl bromide, diethyl sulfate, etc. The amount of alkali used,preferably caustic soda, will be any quantity customarily used by theartin the 'alkylation of cellulose. I have found that it is usuallydesirable to use an amount of alkali within the range of about 5 moles.to about 17 moles and preferably within the range of about 8 moles toabout 14 moles for each mole of cellulose (calculated as CcHmOs)present, depending upon the desired alkoxy content of the product.

In carrying out my invention I may use any type of cellulose materialsuch as, purified wood pulp or cotton linters. The caustic used shouldbe of high purity, altho the presence of sodium chloride is notobjectionable. It is advantageous to use a caustic in granular or flakyform, altho lumps or powder may be used. The amount used will dependmainly upon the degree of etheriflcation desired in the product, and theamount of alcohol used in the reaction mixture. Thus, for example, inthe production of ethyl cellulose having 48-49% ethoxy, the molecularproportion of caustic to cellulose unit (Cal-1100s) is 9:1, while theamount of alcohol should be about 60% by weight of the cellulose. Theamount of alkylating agent used may vary within wide limits. Inpreparing cellulose ethers having good solubility in organic solvents, Iprefer to use a large excess of the alkylating agent. Thus, I may use15-20 moles of alkyl chloride to each cellulose unit. The alkylatingagent serves not only as a reactant but also as a medium for thereaction, and a large part of the excess may be recovered unchanged atthe end of the reaction.

This excess of the alkylating agent may be replaced to a greater orlesser extent by an indifierent organic solvent, such as benzene,toluene, dioxan and the like, which acts both as diluent (medium for thereaction) and as solvent for the I cellulose alkyl ether formed.However, the time required to complete the reaction in the presence ofsuch diluents is greater at anyone temperature than when an excess ofthe alkylating agent serves as medium for the reaction.

The. alcohol used may be a lower aliphatic alcohol, such as for example,methanol, ethanol,

structed for rotating or tumbling motion to effect agitation. Theingredients of the alkylation mixture may be introduced into theautoclave simulalcohol and then removing the excess by pressure.

After all of the ingredients of the alkylation mixture are in theautoclave it is heated either rapidly or gradually to reactiontemperature. I U

find that it is advantageous to heat the mixture very gradually. Adesirable reaction temperature is determined largely byv the reactivityand amount of the alkylating agent present. Thus, when usingethylc'hloride as an alkylating agent, a temperature within the range ofabout 90 C. to about 150 C. and preferably within the range of about 100C. to about 130 C. will be found satisfactory- It will be. found thatthe higher the temperature the more rapid the reaction, while the lowertemperatures insure greater uniformity and higher viscosity of theproduct.

As a further illustration of the method in accordance with thisinvention I may cite the following examples:

Example I Twenty-six grams purified cotton linters and 54 g. sodiumhydroxide in pellets are placed in a nickel-lined autoclave of about 500cc. capac-- ity. A mixture of 20 cc. ethanol and 235 cc. ethyl chlorideare added. After closing the autoclave, it is fastened in a steel framerevolving in an oil bath so that the autoclave is subjected to atumbling motion. The stirring eflect may be increased by placing a fewnickel-lined steel balls in the autoclave. The temperature of the oilbath is constant at 130 C. After five hours heating, the autoclave iscooled below room temperature and its content is gradually introducedinto boiling water. The volatile constituents of the reaction mixturedistil oil and are recovered by condensation, while the product forms awhite, fiocculent precipitate. washed with water until free from salt.The dry product has an ethoxyl content of about 48%.

Example II Twenty-eight grams linters which have been conditioned in100% humidity are treated in a silver-lined autoclave of the sameconstruction and having the same arrangements for heating and agitationas that in Example I, with 54 g. of sodium hydroxide and a-mixture of 20cc. ethanol with 235 cc. ethyl chloride. The temperature is keptconstant at 120 C. for about fifteen hours; the autoclave is then cooledand opened and its contents are transferred into a mixer. By theaddition of hot water, the excess ethyl chloride and the diethyl etherformed as by-product are expelled and recovered by condensation, whilethe ethyl cellulose breaks up into small white crumbs, which are washedwith hot water to remove the salt. The dry product has an ethoxylcontent of 49.3% and its specific viscosity in /2% xylenebutanolsolution (:20 by volume) is 4.31.

Example III Fifty-two grams purified cotton linters of 7% moisturecontent are soaked with 500 cc. ethanol.-

The latter is filtered and the'excess of which is removed by pressingafter 12-24 hours. The weight of the alcohol-wet linters is about 84 g.;10 g. sodium hydroxide and 450 cc. ethyl chloride are added and thewhole is treated in a steam-jacketed, Monel metal autoclave equippedwith mechanical stirrer. The temperature is kept constant at 120 C.,while the stirring is at first, quite slow, and later somewhat faster.After 12-13 hours treatment, the heating is stopped, the volatiles aredistilled OE and the residual mass, still hot, is stirred with hotwater. The product, ethyl cellulose, breaks up into small crumbs, whichare filtered and washed free from salt. The yield is about 69 g., whichis almost of the theoretically possible, when the ethyl cellulose, as inthis case, contains about 48.5% ethoxyl.

Example IV Twenty-six grams purified cotton linters, 300 cc. anhydrousethanol and 60 g. sodium hydroxide in pellets are placed in a bottle andthe whole is fastened in a revolving frame so as to effect tumblingmotion. After 24-36 hours the sodium hy droxide is dissolved and thelinters are pressed to remove the excess alcoholic caustic solution. Theresidual weight of the moist linters is about '70 g. with a causticcontent of about 23 g. Fortysix grams more solid sodium hydroxide and235 cc. ethyl chloride are added and the whole is treated for 15-16hours at C. in one of the autoclaves described in the previous examples.The product is then separated from the reaction mixture according to oneof the methods dezcsrgaed before. It has a specific viscosity of It willbe understood that the details and examples hereinbefore set forth areillustrative only, and the invention as herein broadly'described andclaimed is in no way limited thereby.

What I claim and desire to protect by Letters Patent is:

1. A process for the preparation of an alkyl ether of cellulosecomprising reacting cellulose withan alkylating agent and an alkali, inthe presence of a lower monohydric aliphatic alcohol in amount withinthe range of about 20% to about 90% by weight of the cellulose present.

2. A process for the preparation of an alkyl ether of cellulosecomprising reacting cellulose with an alkylating agent and an alkali, inthe presence of a lower aliphatic alcohol containing the same alkylgroup as contained in the alkylating agent, and in amount within therange of about 20% to about 90% by weight of the cellulose present.

3. A process for producing an alkyl ether of cellulose comprisingreacting cellulose with an alkyl halide and an alkali, in the presenceof an aliphatic alcohol containing an alkyl group corresponding to thealkyl group contained in the.

alkyl halide and in amount within the range of about 20% to 90% byweight of the cellulose present.

4. A process for producing an alkyl ether of cellulose comprisingreacting cellulose with an alkyl halide and an alkali, in the presenceof an aliphatic alcohol containing an alkyl group corresponding to thealkyl group contained in the alkyl halide and in amount within the rangeof about 40% to 70% by weight of the cellulose present.

5. A process for the preparation of an alkyl ether of cellulosecomprising reacting cellulose with an alkylating agent and an alkali, inthe lose which comprises, reacting cellulose with ethyl presence of alower monohydric aliphatic alcohol in amount within the range of about40% to about 70% by weight of the cellulose present. 6. A process forthe production of ethyl cellulosewhich comprises reacting cellulose withethylating agent and an alkali, in the presence of ethanol in amountwithin the range of about 20% to 90% by weight or the cellulose present.

'1. A process for the production of ethyl cellulose which comprisesreacting cellulose with ethyl chloride and an alkali, in the presence.of ethanol in amount within the range of about 20% to 90% by weight ofthe cellulose present.

8. A process for the production of ethyl cellulose which comprisesreacting cellulose with ethyl chloride and an alkali, in the presence ofethanol in amount within the range of about 40% to by weight of thecellulose present.

9. A process for the production of ethyl cellulose which comprisesreacting cellulose withl ethyl chloride and an alkali, in the presenceof ethyl alcohol in' amount within the range of about 20% toabout byweightof the cellulose present and at a temperature within the range ofabout C. to about C. I

10. A process for the production 01 ethylcelluchloride in the presenceof alkaliethyl alcohol and water, the ethyl alcohol'being present inamount within the range of about 20% to about 90% by weight ofthe-cellulose present, and the water being present in amount not inexcess of about 100% by weight of the cellulose present.

11. A process for the production of ethyl cellulosewhich comprisesreacting cellulose with ethyl chloride in the presence of alkali, ethylalcohol and water, the ethyl alcohol: being present in amount within therange of about 40% to 70% by weight of the cellulose present and thewater being present in amount not in excess of about 30% by weight ofthe cellulose present.

. 12. A process for the production of ethyl cellulose which comprisesreacting cellulose with ethyl chioride'in the presence of alkali, ethylalcohol and water at a temperature within the range of about 100 C.toabout 130 0., the ethyl alcohol being present in amount within therange of about 40% to 70% by weightof the cellulose present and thewater being present in amount not in excess of about 30% by weight ofthe cellulosepresent. I

' EUGENE J. LORAND.

